Electric Travelling Vehicle and Grass Mower

ABSTRACT

An electric travelling vehicle including: a motor controller configured to control an electric motor based on displacement of a steering operation part to a forward travel position, a neutral position, and a rearward travel position, a brake controller configured to bring an electromagnetic power-off brake into a released state or a braking state; and a travel state detector configured to detect a travelling state that is accompanied with the released state, a stopped state that is accompanied with the braking state, and a transit stopped state that is accompanied with the braking state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application Nos.2017-200282 and 2017-207189, filed Oct. 16, 2017 and Oct. 26, 2017,respectively, the disclosures of which are hereby incorporated in theirentirety by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an electric travelling vehicleincluding: drive wheels that are driven by power from a power device;and a steering operation part, the power device including electricmotors that are driven by being excited, and electromagnetic power-offbrakes. The present invention also relates to a grass mower, which is,for example, an electric travelling vehicle that is equipped with amower unit that rotates cutter blades, using a mower motor.

2. Description of the Related Art

In an electric travelling vehicle according to Patent Document 1, thetravel driving system that rotates drive wheels using an electric motoris provided with an electromagnetic brake, and upon the electric motorbeing driven in response to a manual operation performed using anaccelerator, the electromagnetic brake simultaneously cancels braking onthe travel driving system. Also, upon an operation performed using theaccelerator being stopped, the electromagnetic brake simultaneouslyactivates braking on the travel driving system. This electric travellingvehicle is also provided with a manual switch that is used to activateor cancel braking performed by the electromagnetic brake. That is, inthis electric travelling vehicle, starting of power supply to theelectromagnetic brake (brake cancellation) and stopping of power supplyto the electromagnetic brake (brake activation) are triggered by amanual operation, and are performed simultaneously with this operation.

The electromagnetic brake that is provided on a motor shaft of theelectric motor of the electric travelling vehicle, or on a transmissionshaft coupled to the motor shaft, is an electromagnetic power-off brakethat is provided with a brake spring that presses an armature against abrake disk using a biasing spring force, and an electromagnetic coilthat releases the armature from the brake disk using an electromagneticforce. An electromagnetic power-off brake is in a braking state when thecoil of the electromagnetic brake is not excited, due to a spring or thelike, and is in a released state when the coil of the electromagneticbrake is excited. Therefore, an electromagnetic power-off brake requiresexcitation the entire time the vehicle travels, and there is an issue ofhigh power consumption. Since the capacity of an on-board battery islimited, power consumption is a significant issue for an electrictravelling vehicle. In addition, a premature braking action performed byan electromagnetic power-off brake places an unnecessary load on theelectric motor and the brake shaft.

In a grass mower, the driver's seat is located in an upper portion of atravelling machine body, and a mower unit is located in a lower portionof the travelling machine body. Therefore, it is difficult for thedriver sitting on the driver's seat to check the driving state of themower unit. Thus, technology for avoiding issues by using a detectionsignal from a sensor that monitors the driving state of the mower unithas been proposed. For example, in an electric lawn mower according toPatent Document 2, a load applied to a mower motor that rotates cutterblades is calculated, and the travel speed is reduced when the loadexceeds a threshold value. Also, an electric lawn mower according toPatent Document 3 is provided with: a mower motor that rotates cutterblades; a thermostat that detects the temperature of the motor; acooling flow path that cools the mower motor; and a cover that opens andcloses the cooling flow path, and when the temperature of the motorrises, the cover is opened and the mower motor is cooled by cooling airthat flows in via the cooling flow path. Thus, the mower motor isprevented from overheating.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP H10-164705A-   Patent Document 2: JP2012-187026A-   Patent Document 3: JP2017-104142A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

One objective of the present invention is to provide an electrictravelling vehicle that appropriately performs excitation control on anelectromagnetic power-off brake according the travel state, and performsbrake control under which unnecessary and non-urgent excitation isavoided.

Technology for avoiding an issue in a motor based on the load on themotor and the temperature of the motor is widely known in the field ofmotor control, and devices and packaged programs for realizing suchtechnology are also commercially available. However, an issue in a powertransmission system that transmits power to cutter blades is likely tobe overlooked until it is visually or aurally checked. Such an issue ina power transmission system may cause a significant damage.

Another objective of the present invention is to provide a grass mowerthat can swiftly detect an issue in a power transmission system of amower unit, instead of an issue in the mower motor.

Means for Solving Problem

An electric travelling vehicle according to one embodiment of thepresent invention includes: a vehicle body; a power device that includesan electric motor that is driven by being excited, and anelectromagnetic power-off brake; a drive wheel configured to be drivenby power from the power device; a steering operation part configured tobe displaced to a forward travel position, a neutral position, and arearward travel position from one to another by a manual operation; amotor controller configured to control the electric motor based ondisplacement of the steering operation part; a brake controllerconfigured to bring the electromagnetic power-off brake into a releasedstate or a braking state; and a travel state detector configured todetect a travelling state that is accompanied with the released state, astopped state that is accompanied with the braking state, and a transitstopped state that is accompanied with the braking state and is atransit state between the stopped state and the travelling state,

wherein a transition from the travelling state to the transit stoppedstate occurs on a condition that, in the travelling state, the steeringoperation part has been returned to the neutral position and apredetermined period of time has elapsed upon a rotational speed of theelectric motor decreasing to a very low rotational speed, and atransition from the transit stopped state to the stopped state and atransition from the stopped state to the transit stopped state occurupon a manual operation being performed.

In conventional electric travelling vehicles, control is performed inorder to selectively create: a travelling state in which anelectromagnetic power-off brake (hereinafter abbreviated as anelectromagnetic brake, except in specific cases) is excited and broughtinto a released state and an electric motor is excited so that a vehiclebody travels; and a stopped state in which excitation of anelectromagnetic clutch is stopped and the electromagnetic clutch isbrought into a braking state and excitation of the electric motor isstopped so that the vehicle body is stopped. With the above-describedconfiguration according to the present invention, a control state calleda transit stopped state is set between a travelling state and a stoppedstate. Thus, a transit stopped state occurs before a transition from atravelling state to a stopped state occurs, and the electromagneticbrake and the electric motor are controlled based on individualconditions so that the timing of controlling the electromagnetic brakeand the timing of controlling the electric motor can be optimized. Forexample, in the process of control in which the driver returns thesteering operation part to the neutral position to reduce the number ofrotations of the electric motor (the vehicle speed) to zero to stop thevehicle body that is travelling, the electromagnetic brake and theelectric motor are not simultaneously controlled. Instead, excitation ofthe electromagnetic brake continues until a predetermined period of timehas elapsed upon the rotational speed of the electric motor decreasingto a very low rotational speed (e.g. within the range from 0 rpm toseveral ten rpm), and excitation of the electromagnetic brake is onlystopped upon the predetermined period of time (e.g. approximately 0.5seconds to 2 seconds) elapsing, so that the electromagnetic brakeperforms braking. This control is automatically performed, and thus atransition from a travelling state to a transit stopped state iscomplete. As a result of control automatically being performed on theelectric motor and the electromagnetic brake, the vehicle bodytransitions from a travelling state to a transit stopped state, and thevehicle body is temporarily stopped. In this automatic control performedon the electric motor and the electromagnetic brake to temporarily stopthe vehicle body, both power saving and safety are considered in abalanced manner. Also, a transition from this transit stopped state to astopped state in which the vehicle is reliably stopped occurs on thecondition that a manual operation is performed. Therefore, the driverhas the intention of fully stopping the vehicle body when bringing thevehicle body into a stopped state.

After the driver returns the steering operation part to the neutralposition to reduce the vehicle body speed, and the control statetransitions from a travelling state to a transit stopped state, when thedriver wishes to set the vehicle body in motion again, the driveroperates the steering operation part in a forward travel direction or arearward travel direction from the neutral position. As a result, thecontrol state transitions from a transit stopped state to a travellingstate. Also in this process of control from a transit stopped state to atravelling state, it is preferable that both power saving and safety areconsidered in a balanced manner when the electromagnetic brake and theelectric motor are controlled. For example, in a preferred embodiment ofthe present invention, a transition from the transit stopped state tothe travelling state occurs at least on a condition that, in the transitstopped state, a predetermined period of time (e.g. 0.1 seconds) haselapsed upon the steering operation part being deviated from the neutralposition.

A preferred embodiment of the present invention includes a brakeoperation part of a manual operation type, and the brake operation partis configured to be switchable to a first position to make a request tobring the power-off brake into the released state, and to a secondposition to make a request to bring the power-off brake into the brakingstate. Using this brake operation part, the driver can manually bringthe electromagnetic brake into a release state or a braking stateaccording to the driver's own will, to stop the vehicle body in anemergency or reliably stop the vehicle body, for example. Furthermore,according to this embodiment, a transition from the transit stoppedstate to the stopped state occurs at least on a condition that, in thetransit stopped state, the brake operation part has been switched to thesecond position (braking), and a transition from the stopped state tothe transit stopped state occurs at least on a condition that, in thestopped state, the brake operation part has been switched to the firstposition (brake releasing). With the former configuration, the drivercan convey an intention to stop the vehicle body to the control system,by operating the brake operation part in such a manner. Considering thedriver's intention to stop the vehicle body, the control system bringsthe vehicle body from the transit stopped state to the stopped state.With the latter configuration, the driver can convey an intention tostart running the vehicle body to the control system, by operating thebrake operation part in such a manner. Considering the driver'sintention to stop the vehicle body, the control system brings thevehicle body from the stopped state to the transit stopped state.

It is possible to perform more appropriate control on the electric motorand the electromagnetic brake by providing various conditions fordetecting the travel state. Therefore, according to one preferredembodiment of the present invention, the travel state detector detectsthe travelling state on a condition that the steering operation part hasdeviated from the neutral position, the electromagnetic power-off brakeis in the released state, the electric motor is in an excited state, andthe brake operation part is at the first position. Furthermore, thetravel state detector detects the stopped state on a condition that thesteering operation part is at the neutral position, the electromagneticpower-off brake is in the braking state, the electric motor is in anunexcited state, and the brake operation part is at the second position.Furthermore, the travel state detector detects the transit stopped stateon a condition that the steering operation part is at the neutralposition, the electromagnetic power-off brake is in the braking state,the electric motor is in an unexcited state, and the brake operationpart is at the first position.

With such a configuration of the present invention, it is possible toprevent the driver from forgetting to operate the brake operation part.In addition, it is possible to save power consumption by automaticallystopping excitation of the electromagnetic brake and the travel motorwhen the vehicle body is temporarily stopped. It is also possible toprevent the electric motor from slightly moving due to a torque loss byactivating the electromagnetic brake before activating the electricmotor.

The brake operation part of a manual operation type is used by thedriver to bring the vehicle body into an emergency stopped state througha braking operation. It is preferable that the above-describedtransition control is applied to such a transition to an emergencystopped state as well. Therefore, in a preferred embodiment of thepresent invention, when the brake operation part is switched from thefirst position to the second position in the travelling state, thepower-off brake enters the braking state and a transition from thetravelling state to an emergency stopped state in which the vehicle bodyis stopped occurs when a predetermined period of time (e.g. within therange of 0.1 seconds to 0.5 seconds) has elapsed upon a no-rotationinstruction being output to the electric motor. With this configuration,when the vehicle body is travelling, it is possible to sufficientlydecelerate the vehicle body before the electromagnetic brake enters thebraking state, and thus it is possible to reduce the amount of workinvolved in braking.

A grass mower according to one embodiment of the present inventionincludes: a mower unit that includes a rotation shaft to which a cutterblade is attached, a mower motor, and a mower power transmissionmechanism that establishes a power transmission path through which powerfrom the mower motor is transmitted to the cutter blade; a mower motorcontroller configured to control the mower motor; a mower drive statedetector configured to detect a drive state of the mower motor; and amower abnormality detector configured to detect an abnormality in thepower transmission path based on a detection signal from the mower drivestate detector.

With this configuration, an abnormality in the power transmission pathis detected based on a detection signal from the mower drive statedetector that detects the drive state of the mower motor. Typically, amotor control system has the function of detecting the drive state ofthe motor in order to appropriately drive the motor and protect themotor. Examples of the motor drive state to be detected include thenumber of rotations of the motor, the temperature of the motor, acurrent flowing through the motor, and load on the motor. If anabnormality occurs in the power transmission path through which poweroutput from the mower motor is transmitted to the cutter blade to rotatethe cutter blade, the abnormality also affects the mower motor connectedto the power transmission path, which results in a change in the drivestate of the motor. The mower abnormality detector detects anabnormality in the power transmission path, i.e. an abnormality in themower power transmission mechanism, based on such a change in the drivestate of the motor. Examples of abnormalities in the power transmissionpath include disengagement between the rotation shaft and the cutterblade, and disengagement of a belt if the mower power transmissionmechanism employs a belt power transmission mechanism.

According to one preferred embodiment of the present invention, themower motor controller forcibly stops the mower motor upon the mowermotor abnormality detector detecting an abnormality. If power iscontinuously supplied even after an abnormality has occurred in thepower transmission path, the abnormality may become more significant orcause a secondary problem. Therefore, it is appropriate to forcibly stopthe mower motor to stop power supply.

One preferred embodiment of the present invention includes a manualoperation part configured to provide the mower motor controller with adrive instruction that is an instruction to drive the mower motor and astop instruction that is an instruction to stop the mower motor fromdriving, and when the mower motor is to be recovered from a forciblystopped state, the stop instruction and the drive instruction that issubsequent to the stop instruction are required to be provided from themanual operation part. With this configuration, if the mower motor isforcibly stopped while the mower motor is driven according to aninstruction provided through an operation performed using the manualoperation part, the mower motor will not be recovered from the forciblystopped state or rotate, unless a stop instruction that is aninstruction to stop the mower motor from driving is provided through anoperation performed on the manual operation part. Thus, it is possibleto avoid an issue such as unexpected rotation of the mower motor duringthe task of eliminating an abnormality in the power transmission path.

In one preferred embodiment of the present invention, the mower motor issupplied with power via an inverter, the mower drive state detector is acurrent detector that is built into the inverter and is configured todetect a current value of the mower motor, and the mower abnormalitydetector detects an abnormality in the mower unit upon the current valuefalling below a predetermined value while the mower unit is driving.Current detection is essential for motor control performed by aninverter. Therefore, in terms of costs, it is preferable that the mowerabnormality detector uses the result of detection received from thecurrent detector built into the inverter. For example, in a case wherethe current value of the mower motor is more than 100 amperes when themower motor is performing work under a load, and is approximately onethird thereof when the mower motor is under no load, if powertransmission is blocked due to disengagement of the power transmissionbelt or the like, the current value of the mower motor will be severalamperes. If the cutter blade and the rotation shaft slip, the currentvalue will be several tens of amperes when the mower motor is performingwork, and is approximately one half thereof under no load. Based on sucha phenomenon, the mower abnormality detector can detect an issue in thepower transmission path.

Based on the specifications of the grass mower, the current value of themower motor when the mower motor is performing work under a load, thecurrent value (the rated value) of the mower motor under no load, andthe current value (or the amount of a drop from the rated value) when apower transmission failure has occurred in the power transmission pathfor the mower unit can be checked in advance through experiments.Therefore, according to one simple embodiment of the present invention,the mower abnormality detector detects, as an abnormality in the powertransmission path, a power transmission failure in the mower powertransmission mechanism or an attachment failure in which the cutterblade and the rotation shaft are improperly attached to each other, uponthe current value falling below the predetermined value while the mowerunit is driving. This configuration is advantageous in terms of costsbecause an abnormality in the power transmission path can be detected bysimply performing a threshold value determination on the current value.Of course, in order to more accurately detect an abnormality in thepower transmission path, it is preferable that the mower abnormalitydetector has the function of detecting an abnormality in the powertransmission path based on changes over time in the detection signalsfrom the mower drive state detector, i.e. fluctuations in the detectionsignals.

Furthermore, the mower abnormality detector may be configured tocalculate the probability of occurrence of an abnormality, using adetection signal from the mower drive state detector other than thecurrent detection signal, or various detection signals including thecurrent detection signal, and to detect an abnormality when theprobability of occurrence of an abnormality exceeds a predeterminedvalue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an electric grass mower, which is an example ofan electric travelling vehicle according to a first embodiment.

FIG. 2 is a schematic plan view showing a power system and a controlsystem of the electric grass mower.

FIG. 3 is a vertical cross-sectional view showing a power transmissionmechanism of the electric grass mower.

FIG. 4 is a functional block diagram showing the control system of theelectric grass mower.

FIG. 5 is a schematic diagram showing transitions between control statesof the control system.

FIG. 6 is a side view of a mid-mount passenger electric grass mowerprovided with a mower unit according to a second embodiment.

FIG. 7 is a plan view of the mower unit.

FIG. 8 is a vertical cross-sectional view of the mower unit.

FIG. 9 is a schematic diagram showing a power system and a controlsystem of the electric grass mower.

FIG. 10 is a functional block diagram showing the control system.

FIG. 11 is a flowchart showing an example of abnormality detection.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

The following describes one specific embodiment of an electrictravelling vehicle according to the present invention with reference tothe drawings. The electric travelling vehicle according to the presentembodiment is an electric grass mower. In the present specification,“front” means forward in the front-rear direction (the travel direction)of the vehicle body, and “rear” means rearward in the front-reardirection (the travel direction) of the vehicle body. Also, a left-rightdirection or a lateral direction means a direction that is orthogonal tothe front-rear direction of the vehicle body and is transverse to themachine body (the width direction of the machine body). “Upper” and“lower” indicate a positional relationship in a perpendicular direction(a vertical direction), and show a relationship with respect to a heightabove ground.

FIG. 1 is a side view of the electric grass mower, and FIG. 2 is a planview schematically showing a control system and a power system of theelectric grass mower.

This grass mower is provided with: front wheels 1 that include a leftfront wheel 1 a and a right front wheel 1 b that are of a caster typeand can freely rotate; drive wheels 2 that include a left rear wheel 2 aand a right rear wheel 2 b; a vehicle body 10 that is supported by thefront wheels 1 and the drive wheels 2; a battery 14 that is located in arear portion of the vehicle body 10; a driver's seat 11 that is locatedforward of the battery 14; and a rollover protection frame 12 that islocated rearward of the driver's seat 11 and stands upright. A mowerunit 3 is suspended from the vehicle body 10 in a space below thevehicle body 1, between the front wheels 1 and the drive wheels 2, suchthat the mower unit 3 can be lifted and lowered by a lifting/loweringlinkage mechanism 13.

A floor plate, on which the driver's feet can be placed, is providedforward of the driver's seat 11. Steering operation parts 15 thatinclude a left steering lever 15 a and a right steering lever 15 b arerespectively provided on the left and right sides of the driver's seat11, each steering lever being swingable about a horizontal swing axisthat extends in a direction that transverses the machine body 10. Abrake operation part 16 of a manual operation type is provided on theleft side of the driver's seat 11.

As shown in FIG. 2, a left motor 21 and a right motor 22, which areelectric motors 20 that supply a rotational force to the left rear wheel2 a and the right rear wheel 2 b, are provided. The rotational speeds ofthe left motor 21 and the right motor 22 are individually changedaccording to the amount of power supplied thereto via an inverter drivemodule 4. Therefore, the rotational speeds of the left rear wheel 2 aand the right rear wheel 2 b can be set different from each other, andthe grass mower can turn using the difference between the speeds of theleft and right rear wheels.

To transmit power between the electric motors 20 and the drive wheels 2,transmissions 23 for travel are provided. Electromagnetic brakes 5,which are electromagnetic power-off brakes, are interposed between theelectric motors 20 and the transmissions 23 to brake power transmissionfrom the electric motors 20 to the transmissions 23. As shown in FIG. 3,in the present embodiment, the output shafts of the electric motors 20function as rotation shafts 50 of the electromagnetic brakes 5, and therotation shafts 50 are coupled to input shafts 24 a of the transmissions23. Power input to the input shafts 24 a of the transmissions 23 istransmitted to rear axles 24 b, which are output shafts of thetransmissions 23, via gear power transmission mechanisms. That is, theelectric motors 20, the electromagnetic brakes 5, and the transmissions23 constitute a power device that transmits power to the drive wheels 2.If wheel motors or the like are employed, it is possible to omit thetransmissions 23.

Each electromagnetic brake 5 includes a fixed core 53, an armature 54, aholding plate 56, and a brake disk 55. The fixed core 53 is fixed to abrake housing 51, and includes an electromagnetic coil 531 and a brakespring 532 that are arranged coaxially with the rotation shaft 50. Thebrake disk 55 is a circular disk that has a boss portion that is coupledto the rotation shaft 50 so as not to be rotatable relative to therotation shaft 50. A friction portion is formed on each side of thebrake disk 55. The armature 54 is a ring plate that is disposedcoaxially with the rotation shaft 50 and is movable in the axialdirection. When the electromagnetic coil 531 is not excited, thearmature 54 is pressed against the brake disk 55 due to the biasingspring force of the brake spring 532, and when the electromagnetic coil531 is excited, the armature 54 is released from the brake disk 55 dueto an electromagnetic force that is greater than the biasing springforce.

The holding plate 56 is a ring plate that is disposed coaxially with therotation shaft 50, and is fixed to the fixed core 53 by coupling rods 57that are distributed at three positions in a circumferential direction.The coupling rods 57 also function as guide rods for the armature 54that moves in the axial direction, and as rods for preventing thearmature 54 from rotating. Therefore, the coupling rods 57 are fittedinto recesses that are provided in the outer periphery of the armature54.

As shown in FIG. 2, the mower unit 3 is of a side discharge typeprovided with three cutter blades (blades), and includes a mower deck 3a and three rotary cutter blades 30. A blade drive mechanism 31 thatrotates the cutter blades 30 includes a cutter blade motor 32, which isan electric actuator, and a cutter blade power transmission mechanism 33that transmits power from the cutter blade motor 32 to the cutter blades30. The cutter blade motor 32 is also supplied with power by theinverter drive module 4.

Grass that has been cut by the cutter blades 30 as a result of the grassmower travelling while rotating the cutter blades 30 is transported bywind generated by wind stirring blades of the cutter blades 30 andbaffle plates, to a lateral end side on which a discharge port islocated, through the inside of the mower deck 3 a, and is dischargedfrom the discharge port located on the lateral end side, laterallyoutward of the mower deck 3 a.

As shown in FIG. 2, a control unit 6 excites the electric motors 20, thecutter blade motor 32, and the electromagnetic brakes 5 based ondetection signals from sensors and switches. Therefore, a left steeringposition detection sensor 80 a that detects a swing position (a forwardtravel position, a neutral position, or a rearward travel position) ofthe left steering lever 15 a, a right steering position detection sensor80 b that detects a swing position (a forward travel position, a neutralposition, or a rearward travel position) of the right steering lever 15b, rotation sensors 81 that respectively detect rotations of the leftmotor 21 and the right motor 22, a brake sensor 82 that detects anoperation position of the brake operation part 16, and so on areprovided.

The control unit 6 is connected to the left steering position detectionsensor 80 a, the right steering position detection sensor 80 b, therotation sensors 81, the brake sensor 82, and so on. The control unit 6supplies brake excitation currents, which excite the electromagneticbrakes 5, to the electromagnetic brakes 5 via a driver (not shown).

The inverter drive module 4 outputs drive currents respectively to theleft motor 21, the right motor 22, and the cutter blade motor 32 toexcite and rotate them, based on control target signals from the controlunit 6.

Next, control functional units related to the electric motors 20, theelectromagnetic brakes 5, and the brake operation part 16 will bedescribed with reference to the functional blocks shown in FIG. 4. Thecontrol unit 6 includes a motor controller 61, a brake controller 62,and a travel state detector 63.

The motor controller 61 generates target control signals for controllingthe left motor 21 and the right motor 22, based on detection signalsfrom the left steering position detection sensor 80 a and the rightsteering position detection sensor 80 b that respectively detectdisplacement of the left steering lever 15 a and displacement of theright steering lever 15 b. Furthermore, the motor controller 61generates a target control signal for controlling the cutter blade motor32. Target control signals are supplied to the inverter drive module 4.The inverter drive module 4 includes an inverter drive signal generator41 and an inverter circuit 42. The inverter drive signal generator 41generates inverter drive signals based on the target control signals.The inverter circuit 42 generates motor excitation currents (drivecurrents) that are supplied to the left motor 21, the right motor 22,and the cutter blade motor 32, based on the inverter drive signals.

The brake controller 62 controls excitation currents to bring theelectromagnetic brakes 5 into a released state (excited) or a brakingstate (not excited). The brake operation part 16 is switchable to afirst position (releasing) to make a request to bring theelectromagnetic brakes 5 into a released state, and to a second position(braking) to make a request to bring the electromagnetic brakes 5 into abraking state. The brake operation part 16 at the first position or thesecond position is detected by the brake sensor 82, and a detectionsignal thus generated is transmitted to the control unit 6.

The travel state detector 63 detects various control states such as atravelling state, a transit stopped state, a stopped state, andemergency stopped states (an emergency stopped state A and an emergencystopped state B have been set in the present embodiment) of the vehiclebody 10. A transit stopped state is a state between a stopped state anda travelling state. When transitioning from a stopped state to atravelling state and when transitioning from a travelling state to astopped state, the vehicle body 10 necessarily undergoes a transitstopped state.

When specific conditions are satisfied in each of the control statesdetected by the travel state detector 63, the control unit 6 controlstransition to another control state. Next, transition to each of thecontrol states, which, in the present embodiment, occurs when specificconditions are satisfied, will be described with reference to FIG. 5.

First, the control states in the present embodiment are defined asfollows.

(1) Travelling State

The brake operation part 16 is at the first position (releasing), thesteering operation parts 15 have deviated from the neutral positions,the electromagnetic brakes 5 are in a released state (excited), and theelectric motors 20 are in an excited state (rotated).

(2) Transit Stopped State

The brake operation part 16 is at the first position, the steeringoperation parts 15 are at the neutral positions, the electromagneticbrakes 5 are in a braking state (not excited), and the electric motors20 are in an unexcited state (not rotated).

(3) Stopped State

The brake operation part 16 is at the second position (braking), thesteering operation parts 15 are at the neutral positions, theelectromagnetic brakes 5 are in a braking state (not excited), and theelectric motors 20 are in an unexcited state (not rotated).

(4) Emergency Stopped State A

The brake operation part 16 is at the second position, the steeringoperation parts 15 have deviated from the neutral positions, theelectromagnetic brakes 5 are in a braking state (not excited), and theelectric motors 20 are in an unexcited state (not rotated).

(5) Emergency Stopped State B

The brake operation part 16 is at the first position, the steeringoperation parts 15 are at the neutral positions, the electromagneticbrakes 5 are in a braking state (not excited), and the electric motors20 are in an unexcited state (not rotated). This state functions as atransit state for returning to a normal travelling or stopped state froman emergency stopped state A.

Conditions for a transition from each state to a specified state are asfollows.

(A) Travelling State to Transit Stopped State

A condition that, in the travelling state, the steering operation parts15 have been returned to the neutral positions (in the presentembodiment, each of the left steering lever 15 a and the right steeringlever 15 b may be located within the range of plus or minus 1% from theneutral position thereof), and a predetermined period of time haselapsed upon the rotational speed of each of the electric motors 20decreasing to a very low rotational speed <Condition a>. The very lowrotational speed is, for example, no greater than 10 rpm, and may bepositive, negative, or zero. The predetermined period of time is, forexample, one second. Upon <Condition a> being satisfied, excitation ofthe electromagnetic brakes 5 is stopped, and the electromagnetic brakes5 enter a braking state.

(B) Transit Stopped State to Travelling State

A condition that, in the transit stopped state, a predetermined periodof time has elapsed upon at least one of the steering operation parts 15deviating from the neutral position thereof <Condition b>. Thispredetermined period of time is, for example, 100 milliseconds. Upon<Condition b> being satisfied, excitation of the electromagnetic brakes5 is started, and the electromagnetic brakes 5 enter a released state.

(C) Transit Stopped State to Stopped State

A condition that, in the transit stopped state, the brake operation part16 has been switched to the second position <Condition c>. If <Conditionc> is satisfied, it means that a braking instruction that is aninstruction to bring the electromagnetic brakes 5 into a braking stateis provided to the brake controller 62 via the brake sensor 82.

(D) Stopped State to Transit Stopped State

A condition that, in the stopped state, the brake operation part 16 hasbeen switched to the first position <Condition d>. If <Condition d> issatisfied, it means that a releasing instruction that is an instructionto bring the electromagnetic brakes 5 into a released state is providedto the brake controller 62 via the brake sensor 82. That is, thiscondition is satisfied at a stage before the electromagnetic brakes 5are brought into a released state.

(E) Travelling State to Emergency Stopped State A

A condition that, in the travelling state, the brake operation part 16has been switched to the second position, and a predetermined period oftime has elapsed upon the number of rotations of the electric motors 20decreasing to zero as a result of the motor controller 61 outputting ano-rotation instruction to the electric motors 20 <Condition e>. Thispredetermined period of time is, for example, 200 milliseconds. Upon<Condition e> being satisfied, excitation of the electromagnetic brakes5 is stopped, and the electromagnetic brakes 5 enter a braking state.

(F) Emergency Stopped State A to Emergency Stopped State B

A condition that, in the stopped state, the brake operation part 16 hasbeen switched to the first position <Condition f>. If <Condition f> issatisfied, it means that a releasing instruction that is an instructionto bring the electromagnetic brakes 5 into a released state is providedto the brake controller 62 via the brake sensor 82. That is, thiscondition is satisfied at a preparatory stage for recovering thetravelling state after the transit stopped state. The electromagneticbrakes 5 are still in a braking state.

(G) Emergency Stopped State B to Emergency Stopped State A

A condition that, in the emergency stopped state A, the brake operationpart 16 has been switched to the second position <Condition g>. If<Condition g> is satisfied, it means that a braking instruction that isan instruction to bring the electromagnetic brakes 5 into a brakingstate is provided to the brake controller 62 via the brake sensor 82.

(H) Emergency Stopped State B to Transit Stopped State

A condition that, in the emergency stopped state B, the steeringoperation parts 15 are returned to the neutral positions <Condition h>.If <Condition h> is satisfied, it means that preparations for returningto the travelling state have been made.

As described above, not only simple control states such as a travellingstate, a stopped state, and emergency stopped states, but also a transitstopped state is set between a travelling state and a stopped state, andthus control over the electromagnetic brakes 5 and the electric motors20 is optimized. Also, the emergency stopped state A and the emergencystopped state B are set as the emergency stopped states, and thuscontrol over a transition from an emergency stopped state to a normaltravelling state and a normal stopped state is optimized.

Other Embodiments Modified from First Embodiment

(1) In the above-described embodiment, the left motor 21 that drives theleft rear wheel 2 a and the right motor 22 that drives the right rearwheel 2 b are provided as the electric motors 20. Instead of thisconfiguration, the electric motors 20 may be replaced with a singlemotor, and the output line from the motor may be divided into left andright lines, and transmissions 23 that each have a continuously variabletransmission device may be provided on the left and right lines,respectively. With this configuration, steering is realized by adjustingthe respective shift positions of the continuously variable transmissiondevices using the left steering lever 15 a and the right steering lever15 b.

(2) The brake operation part 16 may be provided with a lever switch or aseesaw switch that can be selectively set to the first position and thesecond position, or a momentary action type switch or an alternatingaction type switch instead.

(3) According to the above-described embodiment, the electric travellingvehicle is a so-called zero-turn type vehicle in which the left rearwheel 2 a and the right rear wheel 2 b constituting the drive wheels 2can be individually driven. However, the electric travelling vehicle maybe a vehicle in which the left rear wheel 2 a and the right rear wheel 2b are coupled to each other by a differential mechanism. If this is thecase, the electric motors 20 are replaced with a single motor. In thiscase, typically, a steering wheel is used as the steering operationparts 15.

(4) The way in which the functional units shown in the functional blockdiagrams in FIGS. 3 and 4 are distinguished from each other is anexample for facilitating understanding of the descriptions. Severalfunctional units may be integrated into one, and a single functionalunit may be divided into a plurality of units, as appropriate.

(5) In the above-described embodiment, the electric travelling vehicleis a grass mower. However, the electric travelling vehicle may be anagricultural work machine such as a tractor, a combine, or a ricetransplanter. Furthermore, the present invention is applicable to anoff-road vehicle such as a Jeep.

Second Embodiment

The following describes one specific embodiment of a grass moweraccording to the present invention with reference to the drawings. Thegrass mower according to the present embodiment is a mid-mount typeelectric grass mower.

FIG. 6 is a side view of the electric grass mower (hereinafter simplyreferred to as the grass mower). This grass mower is provided with: afront wheel unit 101 that includes a left front wheel 101 a and a rightfront wheel 101 b that are of a caster type and can freely rotate; adrive wheel unit 102 that includes a left rear wheel 102 a and a rightrear wheel 102 b; a vehicle body frame 110 that is supported by thefront wheel unit 101 and the drive wheel unit 102; a battery 107 that islocated in a rear portion of the vehicle body frame 110; a driver's seat111 that is located forward of the battery 107; a rollover protectionframe 112 that is located rearward of the driver's seat 111 and standsupright; and a mower unit 103 that is suspended from the vehicle bodyframe 110 in a space below the vehicle body frame 110, between the frontwheel unit 101 and the drive wheel unit 102, such that the mower unit103 can be lifted and lowered by a lifting/lowering linkage mechanism113.

A floor plate 114, on which the driver's feet can be placed, is providedforward of the driver's seat 111, and a brake pedal 116 protrudestherefrom. Steering units 115 that include a left steering lever 115 aand a right steering lever 115 b are respectively provided on the leftand right sides of the driver's seat 111, each steering lever beingswingable about a horizontal swing axis that extends in a direction thattransverses the machine body. The rotational speed of the left rearwheel 102 a can be changed using the left steering lever 115 a, and therotational speed of the right front wheel 101 b can be changed using theright steering lever 115 b. The rotational speeds of the left rear wheel102 a and the right rear wheel 102 b can be individually changed, and asharp turn can be realized by setting the directions of rotation of therear wheels to be opposite to each other. Therefore, this grass mower isalso referred to as a zero-turn mower.

As shown in FIG. 7, the mower unit 103 is of a side discharge type, andis provided with a mower deck 130 and two rotary cutter blades 120. Theleft cutter blade 120 and the right cutter blade 120 are arranged sideby side in a direction that traverses the vehicle body. The mower deck130 includes a top wall 131, and a front wall 132 and a rear wall 133that extend downward from the outer peripheral edge of the top wall 131.The front wall 132 is continuous with a front portion of the outerperipheral edge of the top wall 131, and the rear wall 133 is continuouswith a rear portion of the outer peripheral edge. Right end areas of thefront wall 132 and the rear wall 133 are cut out so as to form a cutgrass discharge port 135, which is covered by a cover 134. The cutterblades 120 are located in an internal space of the mower deck 130, whichis defined by the top wall 131, the front wall 132, and the rear wall133.

Each cutter blade 120 has a band plate-like shape with cutting edges atboth ends thereof. Also, wind stirring blades are formed on the backside of the cutting edges. During grass cutting work, grass that hasbeen cut by the cutter blades 120 as a result of the grass mowertravelling while rotating the cutter blades 120 is transported throughthe inside of the mower deck 130 by wind generated by the wind stirringblades of the cutter blades 120, while being guided by baffle plateslocated in the mower deck 130, and is discharged laterally outward ofthe mower deck 130 from the grass discharge port 135.

As shown in FIG. 8, rotation shafts 121 that extend downward penetratingthrough the top wall 131 of the mower deck 130 are held by the top wall131 so as to be rotatable, using bearing units 121 a. The cutter blades120 are fastened and fixed to the lower ends of the rotation shafts 121so as to be replaceable, using attachment bolts 121 b. Input pulleys 122are attached to the upper ends of the rotation shafts 121.

As shown in FIG. 7, a mower motor 104 that supplies power to the cutterblades 120 is mounted on a mounting platform 140 that protrudes rearwardfrom the rear wall 133. An output shaft 141 of the mower motor 104 isheld in a vertical orientation inside a motor housing 142 so as to berotatable, using a bearing, and the upper end of the output shaft 141juts out of the motor housing 142. An output pulley 124 is attached tothis jutting portion of the output shaft 141.

A belt 125 is hooked around the input pulleys 122 attached to the tworotation shafts 121, the output pulley 124 attached to the output shaft141 of the mower motor 104, and a tension pulley unit 123 attached tothe mower deck 130. That is, in the present embodiment, a mower powertransmission mechanism MTS that establishes a power transmission pathfor transmitting power from the mower motor 104 to the cutter blades 120is constituted by the output pulley 124 attached to the output shaft 141of the mower motor 104, the belt 125, the tension pulley unit 123, theinput pulleys 122, and the rotation shafts 121 to which the cutterblades 120 are fastened and fixed. If the belt 125 comes off from theinput pulleys 122, the output pulley 124, or the tension pulley unit123, the belt 125 slips, or the cutter blades 120 fastened and fixed tothe rotation shafts 121 come loose, power transmission is at leastpartially blocked, and an abnormality occurs in the power transmissionpath.

FIG. 9 shows a power system and a control system of the electric grassmower. A left motor 181 and a right motor 182, which are travel motorsthat respectively rotate the left rear wheel 102 a and the right rearwheel 102 b, and the mower motor 104, which rotates the cutter blades120, are supplied with power from an inverter 170. The inverter 170includes a travel motor inverter 171 that supplies power to the leftmotor 181 and the right motor 182, and a mower motor inverter 172 thatsupplies power to the mower motor 104. The inverter 170 drives are basedon a control signal from a control device 105. The inverter 170 isconnected to the battery 107, which is a power source.

A mower operation part 190, a left steering angle detection sensor 191a, a right steering angle detection sensor 191 b, a left motor rotationdetection sensor 192 a, a right motor rotation detection sensor 192 b, amower motor rotation detection sensor 193, and a current detector 194are connected to the control device 105.

The mower operation part 190 is a manual operation part that is used todrive the mower motor 104 or stop the mower motor 104 from driving,selectively. In the present embodiment, the mower operation part 190 isconfigured as a swing lever that is swingable to a first position (ON)and a second position (OFF). Upon the mower operation part 190 beingoperated to swing to the first position, an operation position detectionsensor 190 a provides the control device 105 with a drive instruction,which is an instruction to drive the mower motor 104. Upon the moweroperation part 190 being operated to swing to the second position, theoperation position detection sensor 190 a provides the control device105 with a stop instruction, which is an instruction to stop the mowermotor 104 from driving.

The left steering angle detection sensor 191 a detects the swing angleof the left steering lever 115 a. The right steering angle detectionsensor 191 b detects the swing angle of the right steering lever 115 b.The left motor rotation detection sensor 192 a detects the number ofrotations of the left motor 181. The right motor rotation detectionsensor 192 b detects the number of rotations of the right motor 182. Themower motor rotation detection sensor 193 detects the number ofrotations of the mower motor 104.

The current detector 194, which is built into the mower motor inverter172, detects a current flowing through the mower motor 104.

As shown in FIG. 10, the control device 105 receives detection signalsinput from a mower drive state detector 109, a steering state detector191, and a travel state detector 192. The mower drive state detector 109includes the mower motor rotation detection sensor 193, the currentdetector 194, and so on. The steering state detector 191 includes theleft steering angle detection sensor 191 a and the right steering angledetection sensor 191 b. The travel state detector 192 includes the leftmotor rotation detection sensor 192 a and the right motor rotationdetection sensor 192 b.

The control device 105 includes functional units such as an input signalprocessor 151, a left wheel speed calculator 152, a right wheel speedcalculator 153, a travel motor controller 154, a mower motor controller155, a mower abnormality detector 156, and an abnormality notifier 157,and these functional units are built as pieces of hardware or software.The input signal processor 151 has a sensor information processingfunction and an operational input processing function. The input signalprocessor 151 processes external signals from the travel state detector192, the steering state detector 191, the mower drive state detector109, and so on, and converts the signals to pieces of information thatcan be internally used by the control device 105.

The left wheel speed calculator 152 obtains the rotational speed (thenumber of rotations) of the left rear wheel 102 a, i.e. the rotationalspeed (the number of rotations) of the left motor 181, based onoperational information received via the left steering angle detectionsensor 191 a, which detects the amount of movement of the left steeringlever 115 a operated by the driver. Similarly, the right wheel speedcalculator 153 obtains the rotational speed (the number of rotations) ofthe right rear wheel 102 b, i.e. the rotational speed (the number ofrotations) of the right motor 182, based on operational informationreceived via the right steering angle detection sensor 191 b, whichdetects the amount of movement of the right steering lever 115 boperated by the driver.

The travel motor controller 154 provides the travel motor inverter 171with control signals for supplying the left motor 181 and the rightmotor 182 with power that is required to achieve the rotational speed ofthe left motor 181 and the rotational speed of the right motor 182obtained by the left wheel speed calculator 152 and the right wheelspeed calculator 153. The travel motor inverter 171 includes a leftwheel power supplier 171 a and a right wheel power supplier 171 b. Therotational speeds of the left motor 181 and the right motor 182 changeaccording to the amount of power individually supplied thereto by theleft wheel power supplier 171 a and the right wheel power supplier 171b. Therefore, the rotational speeds of the left rear wheel 102 a and theright rear wheel 102 b can be set different from each other, and thegrass mower can turn due to the difference between the speeds of theleft and right rear wheels.

Upon the mower operation part 190 being switched to the first position(ON) and the operation position detection sensor 190 a providing thecontrol device 105 with a first position detection signal, which is adrive instruction and is an instruction to drive the mower motor 104,the mower motor controller 155 controls a mower motor power supplier 172a of the mower motor inverter 172 to drive the mower motor 104.

In the present embodiment, the mower abnormality detector 156 detects anabnormality that has occurred in the power transmission path establishedby the mower power transmission mechanism MTS, based on a detectionsignal from the current detector 194, which is one of the components ofthe mower drive state detector 109. Furthermore, upon the mowerabnormality detector 156 detecting an abnormality that has occurred inthe power transmission path, the mower motor 104 is forcibly stoppedeven if a drive instruction has been input using the mower operationpart 190. Note that, in order to recover the mower motor 104 from aforcibly stopped state, a recovery operation needs to be performed usingthe mower operation part 190. Specifically, the mower operation part 190is first returned from the second position to the first position and aninstruction to stop the mower motor 104 is input to the control device105, and thereafter the mower operation part 190 is switched from thesecond position to the first position and a drive instruction is inputto the control device 105. Thus, the mower motor 104 starts drivingagain.

One specific abnormality detection method that can be employed by themower abnormality detector 156 is to check the current value of themower motor power supplier 172 a, detected by the current detector 194while the mower unit 103 is driving (while the cutter blades 120 arerotating). A current value under a no load condition or a normal loadcondition can be used as a reference value, and a value that is lowerthan this reference value by a predetermined amount can be used as anabnormality detection threshold value. In this case, if the currentvalue falls below the predetermined value (the abnormality detectionthreshold value) despite the mower unit 103 being driven, the mowerabnormality detector 156 can determine that an abnormality has occurredin the power transmission path from the mower motor 104 to the cutterblades 120. In this regard, in order to prevent a sudden drop in thecurrent value, which may be caused by a disturbance or the like, frombeing associated with the occurrence of an abnormality, it is preferablethat an average of current values that have been measured over a periodof time is used as a value that is to be compared with the abnormalitydetection threshold value.

The abnormality notifier 157 notifies the driver of the occurrence of anabnormality when the mower abnormality detector 156 detects anabnormality in the power transmission path, using a display 118 or aspeaker 119 or both. If the mower abnormality detector 156 can discernbetween various types of abnormalities, e.g. between a powertransmission failure in the mower power transmission mechanism MT suchas disengagement of the belt and an attachment failure in which thecutter blades 120 and the rotation shafts 121 are improperly attached,based on the amount of a drop from the reference current value, it ispreferable that the driver is notified of an abnormality such that thedriver can discern the type of abnormality.

Next, the following describes an example of a flow of control fordetecting an abnormality in the power transmission path in the grassmower, with reference to the flowchart shown in FIG. 11.

This flowchart starts from a point in time when the grass mower is in awork standby state (#01). When the grass mower is in a work standbystate, a main SW is ON and the mower operation part 190 is at the secondposition. To transition from a work standby state to a working state,the grass mower first requires that the mower operation part 190 isswitched to the first position (#02). Upon the mower operation part 190being switched to the first position (#02: “Yes” branch), the mowermotor 104 starts rotating. The grass mower stands by until the number ofrotations of the mower motor 104, which has started rotating, reaches arated number of rotations (#03: “No” branch). Although not shown in thisflowchart, if the mower motor 104 does not reach the rated number ofrotations within a predetermined period of time, the mower motor 104 isforcibly stopped. At this time, if the travel motors are driving, thetravel motors are also forcibly stopped. If the mower motor 104 reachesthe rated number of rotations within the predetermined period of time(#03: “Yes” branch), the current value of the mower motor 104 isobtained (#04). The current value thus obtained is compared with anabnormality detection threshold value that has been set in advance(#05). If the current value is no less than the abnormality detectionthreshold value (#05: “No” branch), it is determined that there is noabnormality, and furthermore, whether or not the mower operation part190 has been switched to the second position is checked (#06). If themower operation part 190 has been switched to the second position (#06:“Yes” branch), it means that mowing work has been suspended. Therefore,processing returns to step #01 and the grass mower enters a work standbystate. If the mower operation part 190 has not been switched to thesecond position, i.e. if the mower operation part 190 is still at thefirst position (#06: “No” branch), mowing work continues, and processingreturns to step #04 so that the current value of the mower motor 104 isobtained again.

At determination in step #05, if the current value is less than theabnormality detection threshold value, it is determined that there is anabnormality (#05: “Yes” branch), and the mower motor 104 is forciblystopped (#07). At the same time, the abnormality notifier 157 performsabnormality notification (#08). Subsequently, recovery treatment isperformed to address the abnormality (#09). For example, if theabnormality is disengagement of the belt 125, the belt 125 isre-attached. To return to mowing work after recovery treatment has beencompleted, the grass mower first requires that whether or not the moweroperation part 190 has been switched to the second position is checked(#10). If the mower operation part 190 has been switched to the secondposition (#10: “Yes” branch), the forcibly stopped state is cancelled,and processing returns to step #01 so that the grass mower enters a workstandby state. In step #10, if the mower operation part 190 is still atthe first position (#10: “No” branch), the forcibly stopped state is notcancelled, and the cutter blades 120 do not start rotating.

Other Embodiments Modified from Second Embodiment

(1) The mower abnormality detector 156 may be configured to detect anabnormality using a detection signal from the mower drive state detector109 other than a current detection signal (such as a rotation detectionsignal or a load detection signal). Alternatively, the mower abnormalitydetector 156 may be configured to receive a plurality of input detectionsignals including a current detection signal, calculate the probabilityof occurrence of an abnormality using a calculation module that employsmachine learning or the like, and detect an abnormality when theprobability of occurrence of an abnormality exceeds a predeterminedvalue.

(2) In the above-described embodiment, power from a single mower motor104 is distributed to the two cutter blades 120 by a belt powertransmission mechanism. Instead, the mower motor 104 may be provided foreach of the cutter blades 120. If this is the case, the mower powertransmission mechanism MTS is the rotation shafts 121 that transmitpower from output shafts 141 of the mower motors 104 to the cutterblades 120, and an abnormality that has occurred in the powertransmission path is typically an attachment failure in which the outputshafts 141 and the rotation shafts 121 are improperly attached, or anattachment failure in which the rotation shafts 121 and the cutterblades 120 are improperly attached.

(3) In the above-described embodiment, the power sources of the drivewheel unit 102 are travel motors. However, the travel motors may bereplaced with an internal-combustion engine.

(4) In the above-described embodiment, the mower operation part 190 isof a swing lever type. However, the swing lever may be replaced withanother type of switch such as a seesaw switch or a dial switch.

(5) The grass mower according to the above-described embodiment is amid-mount type grass mower in which the mower unit 103 is locatedbetween the front wheels and the rear wheels. However, the grass mowermay be a front-mount type mower in which the mower unit 103 is locatedforward of the front wheels.

(6) The grass mower according to the above-described embodiment is aso-called zero-turn type vehicle in which the left rear wheel 102 a andthe right rear wheel 102 b included in the drive wheel unit 102 can beindividually driven. However, the grass mower may be a vehicle in whichthe left rear wheel 102 a and the right rear wheel 102 b are coupled toeach other by a differential mechanism.

(7) The way in which the functional blocks shown in FIG. 10 aredistinguished from each other is an example for facilitatingunderstanding of the descriptions. Functional blocks shown in the figuremay be integrated into one, and each functional block may further bedivided into pieces, as appropriate.

Note that the configurations shown in the above-described embodiments(including the other embodiments, the same applies to the following) maybe employed in combination with each other as long as no contradictionsoccur. Also, the embodiments disclosed in the present specification aremerely examples and embodiments of the present invention are not limitedthereto. The embodiments may be modified as appropriate within the scopeof the purposes of the present invention.

1. An electric travelling vehicle comprising: a vehicle body; a powerdevice that includes an electric motor that is driven by being excited,and an electromagnetic power-off brake; a drive wheel configured to bedriven by power from the power device; a steering operation partconfigured to be displaced to a forward travel position, a neutralposition, and a rearward travel position from one to another by a manualoperation; a motor controller configured to control the electric motorbased on displacement of the steering operation part; a brake controllerconfigured to bring the electromagnetic power-off brake into a releasedstate or a braking state; and a travel state detector configured todetect a travelling state that is accompanied with the released state, astopped state that is accompanied with the braking state, and a transitstopped state that is accompanied with the braking state and is atransit state between the stopped state and the travelling state,wherein a transition from the travelling state to the transit stoppedstate occurs on a condition that, in the travelling state, the steeringoperation part has been returned to the neutral position and apredetermined period of time has elapsed upon a rotational speed of theelectric motor decreasing to a very low rotational speed, and atransition from the transit stopped state to the stopped state and atransition from the stopped state to the transit stopped state occurupon a manual operation being performed.
 2. The electric travellingvehicle according to claim 1, wherein a transition from the transitstopped state to the travelling state occurs at least on a conditionthat, in the transit stopped state, a predetermined period of time haselapsed upon the steering operation part deviating from the neutralposition.
 3. The electric travelling vehicle according to claim 1,further comprising: a brake operation part of a manual operation type,the brake operation part being configured to be switchable to a firstposition to make a request to bring the electromagnetic power-off brakeinto the released state, and to a second position to make a request tobring the electromagnetic power-off brake into the braking state,wherein a transition from the transit stopped state to the stopped stateoccurs at least on a condition that, in the transit stopped state, thebrake operation part has been switched to the second position, and atransition from the stopped state to the transit stopped state occurs atleast on a condition that, in the stopped state, the brake operationpart has been switched to the first position.
 4. The electric travellingvehicle according to claim 3, wherein the travel state detector detectsthe travelling state on a condition that the steering operation part hasdeviated from the neutral position, the electromagnetic power-off brakeis in the released state, the electric motor is in an excited state, andthe brake operation part is at the first position, the travel statedetector detects the stopped state on a condition that the steeringoperation part is at the neutral position, the electromagnetic power-offbrake is in the braking state, the electric motor is in an unexcitedstate, and the brake operation part is at the second position, and thetravel state detector detects the transit stopped state on a conditionthat the steering operation part is at the neutral position, theelectromagnetic power-off brake is in the braking state, the electricmotor is in an unexcited state, and the brake operation part is at thefirst position.
 5. The electric travelling vehicle according to claim 3,wherein, when the brake operation part is switched from the firstposition to the second position in the travelling state, theelectromagnetic power-off brake enters the braking state and atransition from the travelling state to an emergency stopped state inwhich the vehicle body is stopped occurs when a predetermined period oftime has elapsed upon a no-rotation instruction being output to theelectric motor.
 6. A grass mower comprising: a mower unit that includesa rotation shaft to which a cutter blade is attached, a mower motor, anda mower power transmission mechanism that establishes a powertransmission path through which power from the mower motor istransmitted to the cutter blade; a mower motor controller configured tocontrol the mower motor; a mower drive state detector configured todetect a drive state of the mower motor; and a mower abnormalitydetector configured to detect an abnormality in the power transmissionpath based on a detection signal from the mower drive state detector. 7.The grass mower according to claim 6, wherein the mower motor controllerforcibly stops the mower motor upon the mower motor abnormality detectordetecting the abnormality.
 8. The grass mower according to claim 7,further comprising: a manual operation part configured to provide themower motor controller with a drive instruction that is an instructionto drive the mower motor and a stop instruction that is an instructionto stop the mower motor from driving, wherein, when the mower motor isto be recovered from a forcibly stopped state, the stop instruction andthe drive instruction that is subsequent to the stop instruction arerequired to be provided from the manual operation part.
 9. The grassmower according to claim 6, wherein the mower motor is supplied withpower via an inverter, the mower drive state detector is a currentdetector that is built into the inverter and is configured to detect acurrent value of the mower motor, and the mower abnormality detectordetects an abnormality in the mower unit upon the current value fallingbelow a predetermined value while the mower unit is driving.
 10. Thegrass mower according to claim 9, wherein the mower abnormality detectordetects, as an abnormality in the power transmission path, a powertransmission failure in the mower power transmission mechanism or anattachment failure in which the cutter blade and the rotation shaft areimproperly attached to each other, upon the current value falling belowthe predetermined value while the mower unit is driving.